main.go

package main

import (
	"encoding/json"
	"fmt"
	"io/ioutil"
	"net/http"
	"os"
	"sync"
)

func stargazers(id string) (int, error) {
	// https://api.github.com/repos/[username]/[repository]
	url := fmt.Sprintf("https://api.github.com/repos/%s", id)

	// Request API to fetch object.
	resp, err := http.Get(url)
	if err != nil {
		return 0, err
	}
	defer resp.Body.Close()
	body, err := ioutil.ReadAll(resp.Body)
	if err != nil {
		return 0, err
	}

	// Apply object from the response body as a JSON.
	data := map[string]interface{}{}
	err = json.Unmarshal(body, &data)
	if err != nil {
		return 0, err
	}

	if v, ok := data["stargazers_count"].(float64); ok {
		return int(v), nil
	}

	return 0, nil
}

func main() {
	list := []string{
		"golang/go",
		"golang/mobile",
		"apple/swift",
		"python/cpython",
		"django/django",
	}

	fmt.Println("\nprintStar")
	for _, id := range list {
		printStar(id)
	}

	fmt.Println("\nprintStarWithChannel")
	printStarWithChannel(list)

	fmt.Println("\nprintStarWithWaitGroup")
	printStarWithWaitGroup(list)
}

func printStar(id string) {
	star, err := stargazers(id)
	if err != nil {
		fmt.Fprintln(os.Stderr, err)
	} else {
		fmt.Println(id, star)
	}
}

func printStarWithChannel(list []string) {
	var (
		done        = make(chan bool)
		concurrency = 0
	)

	for _, id := range list {
		concurrency++
		go func(id string, done chan bool) {
			printStar(id)
			done <- true
		}(id, done)
	}

	for i := 0; i < concurrency; i++ {
		<-done
	}
}

func printStarWithWaitGroup(list []string) {
	var (
		wg = new(sync.WaitGroup)
	)

	for _, id := range list {
		wg.Add(1)
		go func(id string) {
			printStar(id)
			wg.Done()
		}(id)
	}

	wg.Wait()
}